CN110117754B - A kind of multi-media corrosion-resistant steel with yield strength of 500MPa and preparation method thereof - Google Patents

Abstract

The invention discloses a multi-medium corrosion-resistant steel with a yield strength of 500 MPa and a preparation method thereof. P≤0.025%, S≤0.01%, Cu: 0.20-0.40%, Ni: 0.20-0.50%, Cr: 0.50-1.00%, Sb: 0.02-0.12%, Sn: 0.005-0.03%, Nb: 0.02-0.05 %Ti: 0.015～0.025%, Ca: 0.001～0.003%, N≤0.006%, the rest are Fe and inevitable impurities, can resist chloride ion, sulfate and sulfite ion mixed medium corrosion, and its yield strength is above 500MPa , ‑40℃ impact toughness ≥80J, excellent welding performance.

Description

A kind of multi-media corrosion-resistant steel with yield strength of 500MPa and preparation method thereof

technical field

The invention belongs to the field of metal materials, and relates to a multi-medium corrosion-resistant steel with a yield strength of 500 MPa and a preparation method thereof.

Background technique

Weathering steel or atmospheric corrosion-resistant steel, since the United States proposed Cu-P-Cr-Ni weathering steel in 1930, weathering steel and specific corrosion-resistant low alloys have developed rapidly.

At present, a number of patents have been applied for high-strength weathering steel and its manufacturing method at home and abroad, such as "a high-strength weathering steel and its production method" (CN200610125365.2), "a high-strength low-alloy steel" published in 2007 Atmospheric corrosion-resistant steel and its production method" (CN200510111858.6), "a 600MPA high-strength weathering steel and its preparation method" published in 2008 (CN200810026086.X), "a weathering steel" published in 2012 (CN2012 10130225.X), "a manufacturing method of high-strength cold-rolled weathering steel sheet and high-strength cold-rolled weathering steel sheet" (CN2015 1003 2657.0), disclosed in 2015, "High Corrosion Resistant Steel Sheet" (JP04235250A) published in Japan in 1992, The low Cr weathering steels involved in these patents (applications) generally have a Cr content below 0.7% and a Ni content below 0.5%, or use lower Ni (0.11-0.13%) and higher P ( 0.070-0.105%), its corrosion resistance is difficult to meet the practical application requirements of multi-medium harsh corrosive environments.

"A Weathering Steel and Its Manufacturing Method" (CN2009 1004 8141.X) published by China in 2009, the Cr content is generally below 0.7%, the Ni content is below 0.5%, and the Cu is up to 0.8%; Non-quenched and tempered needle-like structure high-strength low-yield-strength-ratio weathering steel and its production method" (CN2009 1018 0490.7) "A high toughness and high weather resistance bridge steel" (CN2010 1060 6201.8), published in 2013 "High-strength weathering steel and its preparation method" (CN2013 1005 0995.8), "Ultra-low Carbon Bainitic Weathering Steel" (US6315946) disclosed in the United States uses low-carbon or ultra-low carbon steel, in addition to conventional corrosion-resistant elements Cu, Cr , Ni and content, add Mo not higher than 0.50%. The grades of yield strength of the steels involved in these patents (applications) range from 450 to 700 MPa. The corrosion resistance coefficient I of the above steel grades is ≤ 6.1, and it has certain atmospheric corrosion resistance.

"A kind of weathering steel with high corrosion resistance and high strength and its manufacturing method" (CN200710045329.X) disclosed by China in 2007, "Weathering steel with yield strength above 700MPa and its manufacturing method" (CN200910056602.8) published in 2009 , "A method of high-strength weathering steel and semi-steel smelting high-strength weathering steel" disclosed in 2014 (CN2014 1081 1126), "Titanium-containing high-chromium weathering steel and its preparation method" (CN2015 10801812.0) disclosed in 2015, "High chromium weathering steel and its preparation method" (CN2015 1080 2484.6) and several other patents (applications), the Cr content is 2.5-10.0%, in order to improve the corrosion resistance, add microalloying element Nb, or Nb+Ti composite microstructure Alloying increases strength, but these patents improve corrosion resistance by increasing Cr, which will greatly reduce the weldability of the steel and increase the cost of the alloy.

"Corrosion Resistant Steel" (JP10025550A) published in 1998, "Corrosion Resistant Steel in the Soil" (JP2000336463) published in 2000, "Corrosion Resistant Steel with Excellent Matrix and Heat Affected Zone Toughness" (JP2002363704) published in 2002, etc. The steel types involved in each of the patents (applications) belong to high Cr weathering steel in terms of composition, and the Cr content is generally above 7%, mostly between 9-14%. The Cr content in the steel grades described in "Cr-Containing Corrosion Resistant Steel for Building and Construction Structure" (JP2002285298) published in 2002 is 5-10%. The Japanese patents "Seawater Corrosion Resistant Steel" (JP01079346A) and "High Corrosion Resistance Strong Magnetic Vibration Alloy" (JP05302148A) belong to high Al weathering steel. In addition to high Al content, it also contains Cr far exceeding the level of ordinary weathering steel.

In addition, in order to improve the strength, the steel grades described in these patents (applications) also contain unequal amounts of Mo, B, Zr, Co, W, etc., and simultaneously add two or three combinations of alloying elements Nb, V, and Ti. , The addition of these elements, on the one hand, increases the manufacturing cost and difficulty, and on the other hand is detrimental to the welding and toughness of the steel plate.

Alloy design is an important part of material design. In order to improve the corrosion resistance of steel, specific alloying elements need to be added to the steel. Each alloying element plays a different role in steel, which is briefly described as follows:

C: C is an interstitial strengthening element and has a significant effect on interstitial strengthening of steel. Adding it to hypoeutectoid steel will precipitate cementite in the steel and increase the micro-region potential difference of the steel in a corrosive environment, which is detrimental to the corrosion resistance of the steel. At the same time, C affects the welding performance, stamping performance and impact toughness of steel.

Cu: Cu is a solid solution strengthening element in steel, and when the content is high, it will produce a precipitation strengthening effect. When 0.2% to 0.4% Cu is added to the steel, it has superior corrosion resistance than ordinary carbon steel in rural atmosphere, industrial atmosphere or marine atmosphere. Cu can be enriched on the surface of the steel and in the rust layer, which can promote the passivation of the steel anode. Cu can also form a barrier layer with Cu and P as the main components between the substrate and the rust layer. Has better protection. In addition, Cu has the obvious effect of offsetting the harmful effects of S in steel. The higher the content of S in steel, the more significant the relative effect of alloying element Cu in reducing the corrosion rate. It is generally believed that this is due to the formation of insoluble sulfides between Cu and S. .

P: P is an interstitial strengthening element, but reduces the low temperature toughness of steel. P is also one of the most effective alloying elements to improve the atmospheric corrosion resistance of steel. Generally, when the content of P is 0.08% to 0.15%, the corrosion resistance is the best. When P and Cu are jointly added to the steel, a better recombination effect is shown. Under atmospheric corrosion conditions, P in the steel is an anodic depolarizer, which can accelerate the uniform dissolution of the steel and the oxidation rate of Fe ²⁺ in the steel, and help to form a uniform α-FeOOH rust layer on the steel surface, Promote the formation of amorphous iron oxyhydroxide FeO _x (OH) _3-2x dense protective film, thereby increasing the resistance, becoming a protective barrier for corrosive media to enter the steel matrix, and preventing the interior of the steel from atmospheric corrosion. It also acts as a corrosion inhibitor when P forms PO ₄ ^3- .

Cr: Cr is a solid solution strengthening element, and its solid solution strengthening ability is slightly lower than that of Mn, and it has no obvious effect on the toughness of the material. Cr can form a dense oxide film on the steel surface and improve the passivation ability of the steel. The Cr content in weathering steel is generally 0.4 to 1.0% (up to 1.3%). When Cr and Cu are added to the steel at the same time, the effect is particularly obvious. Some studies have pointed out that the increase of Cr content is conducive to refining α-FeOOH. When the Cr content in α-FeOOH at the rust layer/metal interface exceeds 5%, it can effectively inhibit the intrusion of corrosive anions, especially ^Cl- ; at the same time, adding Cr element It can also prevent the conversion of Fe ³⁺ to Fe ²⁺ during drying, thereby improving the weather resistance of the steel. But in areas with high Cl ^- content, the addition of Cr element is considered to be harmful.

Mn: There is no consensus on the effect on corrosion resistance. Many scholars believe that Mn can improve the corrosion resistance of steel in the marine atmosphere, but it has no effect on the corrosion resistance in the industrial atmosphere. The Mn content in weathering steel is generally 0.5% to 2%.

Si: Si is a replacement solid solution strengthening element, which is beneficial to improve the yield limit and strength of steel. The use of other elements such as Cu, Cr, P, and Ca can improve the weather resistance of the steel, and the higher Si content is conducive to refining α-FeOOH, thereby reducing the overall corrosion rate of the steel.

Ni: It is a relatively stable element, and Ni alloying is also beneficial to improve the low temperature impact toughness of steel. The addition of Ni can change the self-corrosion potential of the steel to the positive direction, which increases the stability of the steel. The atmospheric exposure test shows that when the Ni content is about 4%, the atmospheric corrosion resistance of coastal weathering steel can be significantly improved.

Al: Al is a substitutional solid solution strengthening element, and can also form AlN precipitates with N in the steel, resulting in a certain degree of grain refinement strengthening and precipitation strengthening effects. Al mainly forms a stable spinel complex oxide (FeAl ₂ O ₄ ) in the spinel oxide (Fe ₃ O ₄ ) of the inner rust layer, which makes the rust layer have cation selectivity to inhibit the intrusion of Cl ^- . Si-Al alloying has been used in recent years to develop low-cost weathering steels.

Mo: Mo is a strong carbide former and a solid solution strengthening element in steel. The dissolved Mo in the steel is hydrolyzed to FeMoO ₄ to inhibit the anodic reaction, and the MoO ₄ ^2- ion makes the rust layer have cation selectivity, which effectively inhibits the passage of Cl ^- and thus improves the anti-Cl ^- corrosion ability of the steel. When the steel contains 0.4% to 0.5% Mo, the corrosion rate of the steel in the atmospheric corrosion environment (especially the industrial atmosphere) may be reduced by more than half.

W: W is a strong carbide forming element and is also a solid solution strengthening element in steel. W increases the polarization resistance of the rust layer through FeWO ₄ and suppresses the anodic reaction. The WO ₄ ^2- ion makes the rust layer have cation selectivity, effectively inhibits the passage of Cl ^- , and further improves the corrosion resistance of steel by Cl ^- . It is worth noting that the inhibitory effects of W and Mo on steel corrosion are different under different acidic electrolytes and _O2 concentrations.

Sb, Sn: Sb and Sn can increase the polarization resistance, reduce the corrosion rate of low alloy steel in HCl solution, and can form Sb ₂ O ₅ and SnO ₂ protective layers on the steel surface, effectively inhibiting the progress of cathodic corrosion reaction. In addition, the combination of Sb and Cu can make the low carbon steel have a lower corrosion rate than the steel containing Sb or Cu alone when it is corroded with sulfuric acid solution. Sb and Sn have little effect on the strength of steel and have an adverse effect on low temperature toughness.

Co: Co is a substitutional solid solution strengthening element, but it does not contribute much to the strength. Co can promote the diffusion of C atoms in steel and increase the rate of phase transformation. Some recent studies suggest that the enrichment of Co in the stable rust layer can effectively inhibit the intrusion of Cl ^- and improve the corrosion resistance of steel in the marine atmosphere.

S: It has an adverse effect on weather resistance, and its content is controlled to be less than 0.04% as a residual element.

Ca: Adding a small amount of Ca to weathering steel can not only significantly improve the overall atmospheric corrosion resistance of the steel, but also effectively avoid the rust sag phenomenon that occurs when the weathering steel is used. A small amount of Ca is added to the weathering steel to increase the alkalinity of the corrosion interface, reduce its erosiveness, and promote the transformation of the rust layer into dense and protective α-FeOOH. WT Jeong ^[34] et al. pointed out that the effect of Ca is better when combined with Si.

Rare earth element (RE): RE element is one of the additive elements of weathering steel without Cr and Ni. Usually the amount of RE added is less than or equal to 0.2%. RE element is an extremely active element, and is a strong deoxidizer and desulfurizer, which mainly purifies steel. The addition of RE elements can refine the grains, change the state of inclusions in the steel, reduce the number of harmful large inclusions, and reduce the source of corrosion, thereby improving the atmospheric corrosion resistance of the steel.

Nb: Nb element can change the morphology of the rust layer, increase the corrosion potential, and reduce the corrosion rate of steel. Studies have shown that after the steel is treated with solid solution niobium, the corrosion resistance in the marine atmospheric corrosion environment will be improved. High-strength weathering steel with strength higher than 450MPa (such as Q450NQR1 of 450MPa grade, Domex series weathering steel of 600-700MPa grade) is generally selected to add Nb as the main microalloying element to refine the grain and improve the strength. Studies have shown that Nb can significantly inhibit the precipitation of Mo and Cr in super martensitic stainless steel 13Cr, prevent the appearance of Mo-depleted and Cr-depleted areas, and improve the pitting corrosion resistance of the steel.

Ti: Ti is added to the steel, and Ti can form carbonitrides with C and N, which are precipitated during the hot rolling of the steel, refine the austenite grains, and achieve the purpose of precipitation strengthening. At the same time, Ti will also form with S in the steel. The compound, which precipitates at high temperature, avoids the formation of MnS and reduces the corrosion resistance. In addition, the coexistence of Ti also reduces the size of α-FeOOH crystals.

V: V or VN alloying can effectively reduce the corrosion rate of weathering steel, make it have excellent pitting corrosion resistance, make the corrosion more uniform on the surface of the steel substrate, improve the charge conduction resistance of the rust layer, and enhance the insulation performance. The analysis of the rust layer of VN alloyed weathering steel shows that the content of α-FeOOH is higher, and the value of α-FeOOH/γ-FeOOH is larger, which once again shows that VN alloying is conducive to the formation of a thermodynamically stable rust layer. In addition, in V or VN alloyed low carbon steel, the VN particles precipitated at high temperature show good precipitation strengthening and grain refinement strengthening, and the contribution rate of the sum of the two to the yield strength is as high as 70%.

In the design of material structure, it is necessary to consider the phase composition (ferrite, pearlite, bainite or martensite, and various precipitates) and volume fraction of the material, and the size of each phase (grain size, interlamellar spacing) or slat spacing or length) etc. These structural characteristic parameters directly affect the conventional mechanical properties, fatigue properties, corrosion properties and so on of the material. Ferrite refines the grains, reduces the potential difference of each phase in the steel, and can also effectively improve the corrosion resistance of the steel. Therefore, the manufacturing process also plays an important role in improving the mechanics and corrosion resistance of the steel.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a multi-medium corrosion-resistant steel with a yield strength of 500 MPa and a manufacturing method. This low-alloy steel has the corrosion resistance of chloride ion, sulfate and sulfite ion mixed medium.

A multi-media corrosion resistant steel with a yield strength of 500 MPa, the chemical composition constraint range is C: 0.06-0.10%, Mn: 0.70-1.20%, Si: 0.15-0.40%, P≤0.025%, S ≤0.01%, Cu: 0.20-0.40%, Ni: 0.20-0.50%, Cr: 0.50-1.00%, Sb: 0.02-0.12%, Sn: 0.005-0.03%, Nb: 0.02-0.05%, Ti: 0.015- 0.025%, Ca: 0.001～0.003%, N≤0.006%, the rest are Fe and inevitable impurities.

Further, the total amount of Sb+Sn of steel grades is controlled to be between 0.05 and 0.12%, and the corrosion resistance of sulfate and sulfite ions is exerted; the total amount of Cu+Ni+Cr is between 1.20 and 1.65%, and Cu:Ni =1:1.1～1:1.5, exert the effect of resistance to chloride ion, sulfite ion and atmospheric corrosion, and improve the surface quality of steel; the total amount of Nb+Ti is between 0.035-0.065%, exerting strong and toughness, and enhancing weldability and resistance to chloride ion corrosion.

Further, the manufacturing method of the multi-medium corrosion-resistant steel with a yield strength of 500 MPa includes the following steps: through the process of molten iron desulfurization-converter smelting-LF refining-VD and/or RH treatment-continuous casting process, the obtained continuous Casting billet, continuous casting billet is reheated to 1180～1220℃, rough rolling finish rolling temperature ≥1020℃, finishing rolling outlet temperature 820-860℃, after rolling, it is cooled to about 560～650℃ at a speed of 5～22℃/s , then air cooling or slow cooling.

Further, the microstructure of the multi-media corrosion-resistant steel with a yield strength of 500 MPa is a small amount of polygonal ferrite + acicular ferrite + bainite.

Further, the multi-media corrosion-resistant steel with a yield strength of 500 MPa has the corrosion resistance of chloride ion, sulfate and sulfite ion mixed media, and the corrosion rate is lower than 1/10 of that of ordinary low-alloy steel Q345B. .

Further, the said one kind of corrosion-resistant steel with a yield strength of 500MPa grade, the yield strength of the hot-rolled steel plate is ≥500MPa, the tensile strength is ≥600MPa, the elongation is ≥18%, and the V-notch impact is under the condition of -40 ℃. Work ≥ 80J.

Beneficial effects of the present invention:

1) The 500MPa grade multi-media corrosion-resistant steel of the present invention has the corrosion resistance of chloride ion, sulfate and sulfite ion mixed medium, and is more resistant to atmospheric corrosion, chloride ion corrosion, or sulfate ion corrosion than conventional ones. Steel, its comprehensive corrosion resistance is better.

2) With the design of lower alloy composition, the carbon equivalent Ceq of steel is less than or equal to 0.45%, and Pcm is less than or equal to 0.20%, and the welding performance can also be guaranteed.

3) Compared with 450MPa and weathering steel, the strength is greatly improved, and it has good low temperature impact toughness, which meets the use of mechanical equipment under extremely cold conditions.

4) The alloy cost of steel is low, and the production difficulty of continuous casting and hot rolling is relatively small.

Detailed ways

The following are specific embodiments of the present invention:

After the process of molten iron desulfurization - converter smelting - LF refining - VD and/or RH treatment - continuous casting, the obtained continuous casting billet is reheated to 1180 ~ 1220 ° C, the rough rolling and finishing rolling temperature is ≥ 1020 ° C, and the finishing rolling is exported. The temperature is 820-860°C, and after rolling, it is cooled to about 560-650°C at a rate of 5-22°C/s, and then air-cooled or slowly cooled.

The chemical composition of the embodiment of table 1

The continuous casting billet is reheated to 1180-1220℃, the final rolling temperature of rough rolling is ≥1020℃, the exit temperature of finishing rolling is 820-860℃, after rolling, it is cooled to about 560-650℃ at a speed of 5-22℃/s, and then air-cooled Or slow cooling, the properties of the prepared steel sheets are shown in Table 2.

The mechanical properties of the embodiment of table 2

The corrosion resistance of the steel was tested by the full immersion corrosion test. The parameters of the corrosion test are:

1) Corrosion solution 0.01mol/L NaHSO3, saturated NaCl solution;

2) 2PH is controlled between 4.3 and 4.4;

3) Solution temperature: 45℃;

4) Humidity: Air humidity.

Corrosion rate calculation formula:

In the formula: V _w - weight loss corrosion rate, g/m ² ·h;

ΔW—weight loss, g;

S—surface area of corrosion sheet, m ² ;

T-corrosion time, h.

The Q450 and Q345B were subjected to full immersion corrosion experiments in the same environment.

Corrosion rate (g/m ² ·h) of the embodiment in Table 2

The above description is only a specific and exemplary description of the present invention. It should be noted that the specific implementation of the present invention is not limited by the above methods, as long as various non-substantial improvements made by the technical ideas and technical solutions of the present invention are adopted. , or the technical idea and technical solution of the present invention are directly applied to other occasions without improvement, all within the protection scope of the present invention.

Claims (2)

1. A variety of medium corrosion-resistant steel with a yield strength of 500MPa, characterized in that the weight percent of its chemical composition is C: 0.06~0.10%, Mn: 0.70~1.20%, Si: 0.15~0.40%, P≤0.025 %, S≤0.01%, Cu: 0.20~0.40%, Ni: 0.20~0.50%, Cr: 0.50~1.00%, Sb: 0.02~0.12%, Sn: 0.005-0.03%, Nb: 0.02~0.05% Ti: 0.015~0.025%, Ca: 0.001~0.003%, N≤0.006%, the rest are Fe and inevitable impurities; The total amount of Sb+Sn is between 0.05-0.13%; the total amount of Cu+Ni+Cr is between 1.20-1.60%, and Cu:Ni=1.3:1-2:1; the total amount of Nb+Ti is 0.035-0.065 %between; The microstructure of the obtained steel is a small amount of polygonal ferrite+acicular ferrite+bainite; The obtained steel is a multi-media corrosion resistant steel with a yield strength of 500 MPa, and has the corrosion resistance of chloride ion, sulfate and sulfite ion mixed medium; The yield strength of the obtained hot-rolled steel sheet is ≥500MPa, the tensile strength is ≥600MPa, the elongation is ≥18%, and the V-notch impact energy is ≥80J at -40°C. 2. a preparation method of the multiple medium corrosion resistant steel of yield strength 500MPa grade as claimed in claim 1, it is characterized in that preparation step is: through molten iron desulfurization-converter smelting-LF refining-VD and/or RH processing- Continuous casting process, the obtained continuous casting billet, the continuous casting billet is reheated to 1180～1220℃, the final rolling temperature of rough rolling is ≥1020℃, the exit temperature of finishing rolling is 820～860℃, and the speed after rolling is 5～22℃/s Cool to 560-660°C, then air-cool or slow-cool.